1. Field of the Invention
Aspects of the present invention relate to a pouch-type secondary battery including a pouch case having bent sealing portions, to cover edges of a battery cell, and to buffer external impacts.
2. Description of the Related Art
Generally, a lithium polymer battery refers to a battery including an electrode assembly, which includes a separator disposed between a positive plate and a negative plate. The separator electrically isolates the plates, and includes an ion-conducting medium, i.e., an electrolyte. Such a separator is formed of a gel polymer that is impregnated with the electrolyte, in order to improve ionic conductivity. The gel polymer electrolyte provides various advantages, such as, excellent adhesion to electrodes, superior mechanical properties, and ease of manufacturing, in addition to improved ionic conductivity.
A lithium polymer battery can be fabricated in the form of a plate-like structure, so there is no need to adopt a winding process, which is necessarily involved in manufacturing some lithium ion batteries. As a result, the electrode assembly can be in the form of a stacked, plate-like structure, and it is also possible to fabricate the electrode assembly as a square-shaped structure. Further, there is substantially no electrolyte exposed to the outside, due to an internal injection of the electrolyte into the cell, which is fabricated as an integral structure. In addition, the electrode assembly can be processed into a plate-like structure, so there is no need to apply pressure to shape the electrode assembly into a rectangular structure. Consequently, it is possible to use a thin and flexible pouch case instead of a thicker, harder square-shaped, or cylindrical can to house the battery.
As discussed above, when the flexible pouch case is used, it is possible to significantly reduce a thickness of the battery, as compared to using a can. As a result, it is possible to form much larger numbers of the electrode assemblies in the same volume. That is, the battery capacity can be greatly increased. Further, due to the flexibility of the pouch case, it is possible to easily fabricate the battery in a desired form. Therefore, the thus-fabricated battery is readily mounted in a variety of electronic devices.
However, despite the increased battery capacity and shape-ability, a pouch case suffers from problems associated with poor mechanical strength, and is thereby vulnerable to external impacts. In particular, when a large-area pouch-type secondary battery is dropped, a relatively greater impact force is applied to edges of the battery. Impacts to the edges of the battery result in various problems, such as, tearing of the pouch case by the electrode assembly, and opening of sealing portions of the pouch case.